OK i petitioned this the otherday and got No help from NCSoft do a check file and initalize the interface, while out hunting u pick up stuff and it doesn't go into your inventory. Normally it's never and issue cause all you get is cokes or metalic fibre. today I got a moirai gaiters out in plains for lizardmen. i have a screen shot of the shout u picked up Moriar gaiters. but that is it no yellow chat you obtains moirai gaiters. and of course no moriai giaters in the inventory.....
Perhaps you were in a party and another party member got it?
In his screenie he was not in a party. But since the chat box texts were scrolled, maybe he was in a party before.
You can also do a Inventory Auto Arrange, that little button on the top right corner of the inventory UI scroll bar. This worked for me the last time a drop did not appear.
I had that already several times (and I had players in party for which it happened, e.g. for seal stones in a cata). Usually it only happens for one particular type of item - it simply does not show up in inventory, and if you look at the system log, you do not even see a message that this particular player picked up an item (i.e. if you have "by turn", that player seems to be simply skipped, but also nobody else got the item).
Once I had it when we were on HB, for Darion's badges. When I picked them up, they simply seemed to vanish, which was pretty convenient, because they weigh a lot and we had finders keepers loot setting with me picking up, because I have HB quest stage 3 (my inv weight did not go up either). When I relogged, they were in the inventory, and my weight % went up by 10% or so :D
Once I had it when we were on HB, for Darion's badges. When I picked them up, they simply seemed to vanish, which was pretty convenient, because they weigh a lot and we had finders keepers loot setting with me picking up, because I have HB quest stage 3 (my inv weight did not go up either). When I relogged, they were in the inventory, and my weight % went up by 10% or so :D
I know someone that had the issue with arrows, by the time he relogged he was at 160%ish of weight.